The present disclosure is related to a control system for a power drive speed control for a self-propelled patient-support apparatus.
In a clinical environment such as a hospital, for example, the use of self-propelled patient-support apparatuses helps reduce the potential for injury to caregivers by limiting the amount of force required to move a patient-support apparatus throughout the hospital. Such apparatuses include a drive mechanism employing a motorized wheel or track which deploys from a frame to contact the floor. When not in use, the drive mechanism is stowed within the confines of the frame. Activation of the drive mechanism causes the drive mechanism to lower until the wheel or track contacts the floor. Operation of the drive mechanism is controlled by a user from a user interface positioned at a head end or foot end of the patient-support apparatus. The input to the drive motor can be a discrete input such as a momentary switch which causes the drive mechanism to operate at a particular speed/power level. It is a also known to use a variable input which is responsive to an input forced by the user to vary the speed of the patient-support apparatus based on the deflection of the input.
In the case of the momentary switch type input, it is necessary for the designer of the drive mechanism to develop a power level which is acceptable over all ranges of use of the patient-support apparatus. If the load on the patient-support apparatus is greater, the speed at which the drive mechanism is able to drive the patient-support apparatus is limited based on the load. However, this type of motor control is relatively simple to employ.
In the case of the variable-type input, the motor/power control system must be responsive to the variable input to increase or decrease the speed at which the drive mechanism drives the patient-support apparatus. In some cases, the variable input requires a user to push again push handles on the patient-support apparatus to cause the drive mechanism to propel the patient-support apparatus. As the patient-support apparatus moves away from the user, the user must walk at a speed which matches the desired speed of the patient-support apparatus in order to maintain a constant input into the variable-type input. Variations in the speed of the user as compared to the patient-support apparatus tend to cause the user to have difficulty in maintaining a constant input to the variable-type input, thereby causing variations in to the input of the control system and may cause the patient-support apparatus to lurch when the variable input is erratically applied by the user.